700. Search in a Binary Search Tree

/*
// Given the root node of a binary search tree (BST) and a value. 
// You need to find the node in the BST that the node's value equals the given value. 
// Return the subtree rooted with that node. 
// If such node doesn't exist, you should return NULL.

// For example, 
// Given the tree:
        4
       / \
      2   7
     / \
    1   3

// And the value to search: 2
// You should return this subtree:
      2     
     / \   
    1   3

// In the example above, if we want to search the value 5, since there is no node with value 5, we should return NULL.

// Note that an empty tree is represented by NULL, therefore you would see the expected output (serialized tree format) as [], not null.
*/

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode searchBST(TreeNode root, int val) {
        if (root == null) {
            return null;
        }
        
        if (val == root.val) {
            return root;
        }
        else if (val > root.val) {
            return searchBST(root.right, val);
        }
        
        return searchBST(root.left, val);
    }
}